Cathode ray device



Dec. 17, 1968 susuMu YosHlDA ETAL 3,417,199

CATHODE RAY DEVICE Susumu Yoshida, S erLrL` ML'yaoka., Hiroshi, Sahara@ by W/ Affi-15s.

Dec 17, 1968 susuMu YosHlDA ETAL 3,417,199

CATHODE RAY DEVICE 2 Sheets-Sheet z Filed Oct. 22, 1964 C41 c `0 Video INFM-T Vo/T'age 4, VLdeo nPuI' Voll-age C4] Vide o lnpuf Vo/'age Video n/.aul' Voltaje 64] InzEl-Lfars Susanna 4Yoshida. Senz/d Mdyaoka, n *A Hiroshi Sahara., BHW@ W /bm/ Hitt-Lgs.

United States Patent O 3,417,199 CATHODE RAY DEVICE Susumu Yoshida, Senri Miyaoka, and Hiroshi Sahara,

Tokyo, Japan, assignors to Sony Corporation, ShinagaWa-kll, Tokyo, Japan, a corporation of Japan Filed Oct. 22, 1964, Ser. No. 405,743 Claims priority, application Japan, Oct. 24, 1963, E38/56,941 10 Claims. (Cl. 178-7.2)

ABSTRACT F THE DISCLOSURE A system for improving the focusing of an electron beam inA a cathode ray tube which decreases the divergence of the beam by the use of an auxiliary grid upon which is placed a video signal which is out of phase with the signal on the control grid.

This invention relates to a system for providing constant focusing of a modulated electron beam, and more particularly to a system for providing constant focusing of an electron beam found in a cathode ray tube.

Cathode ray tubes generally have associated therewith an electron gun device which is positioned in the neck portion of the tube. A modulated electron beam is emitted from the electron gun device and projected toward a phosphor screen, thereby producing light energy at the point where the electron beam impinges on the phosphor screen.

Itis well known that focusing of an electron beam as it moves toward the screen can be accomplished by two concentration elds, which are herein dened as mainconcentration and pre-concentration.

In cathode ray tubes generally, different multigrid electrode configurations may be used to produce the necessary pre-concentration field for electron beam focusing. Of these electrode configurations those most commonly used are three-grid, four-grid and tive-grid arrangements, hereinafter referred to as triode, tetrode and pentrode confgurations. Of these congurations, the tetrode has been particularly troublesome, for a phenomenon known as blooming occurs at the point of impingement of the electron beam on the phosphor screen. This phenomenon causes poor reproduction of video intelligence.

All of the after-mentioned prior art types of electrode systems used in cathode ray tubes fail to take into consideration the divergence of an electron beam caused by electron beam density. The angle of divergence of the electron beam will vary inversely with the density of electrons in the beams, and thereby cause defocusing at the phosphor screen. This in turn will produce poor reproduction of bright picture signals.

It is, therefore, an object of the present invention to provide an improved cathode ray tube wherein defocusing due to Variations in beam density is substantially eliminated.

Another object of the present invention is to provide a cathode ray tube wherein the density-modulated electron beam can be focused into a sharp image on the phosphorous screen by means of a main-concentration field, which main-concentration eld provides constant electron beam divergence independent of electron beam density.

Another object of the present invention is to provide a cathode ray tube in which the pre-concentration of the electron beam is eifected electrostatically, and the mainconcentration of the electron beam is effected either electrostatically or electromagnetically.

Still another object of the present invention is to provide an improved cathode ray tube having a greatly improved electron gun.

Another and further object of the present invention is to provide an electron beam device wherein the divergence angle of the electron beam is held constant independent of electron beam density.

A still further object of the present invention is to provide an electron beam device which has an improved system for pre-concentration of the electron beam produced therein.

These and other features, advantages and additional objects of the present invention will become manifest to those ordinarily skilled in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings in which like reference characters indicate like parts. The preferred embodiment of the present invention is shown in the following drawings in which:

FIGURE 1 is a diagrammatic representation of a typical prior art electron gun having triode-grid configuration;

FIGURE 2 is a diagrammatic representation of a triode-grid electron gun embodying the novel teachings of the present invention and having included therein an auxiliary grid;

FIGURE 3 is a diagrammatic representation of a prior art pentode-grid electron gun;

FIGURE 4 is a diagrammatic representation of a pentode-grid electron gun having an auxiliary grid therein and embodying the novel teachings of the present invention;

FIGURE 5 is a diagrammatic representation of a prior art tetrode-grid electron gun;

FIGURE 6 is a diagrammatic representation of a tetrode-grid electron gun having an auxiliary grid therein and embodying the novel teachings of the present invention;

FIGURE 7 is a graphical representation showing the relative divergence angle of an electron beam with respect to electron beam density;

FIGURE 8 is a graphical representation showing the difference between signals applied to the cathode of the electron gun and signals applied to a main-concentration iield;

FIGURE 9 is a graphical representation similar to that shown in FIGURE 8 but where the signal applied to the main-concentration field is in proportion to the signal applied to the pre-concentration field;

FIGURE 10 is a diagrammatic representation of a prior art triode-grid electron gun similar to FIGURE 1 but wherein the first grid is cup shape;

FIGURE 11 is a diagrammatic representation of a triode-grid electron gun having an auxiilary grid and embodying the novel teachings of the present invention;

FIGURE 12 is a graphical representation showing the difference between signals applied to the cathode of an electron gun and the signals applied to the main-concentration field of the electron gun; and

FIGURE 13 is a graphical representation similar to that of FIGURE 9 except that the signals shown are of the opposite polarity.

In order to appreciate the present invention it is deemed advisable to make reference to certain prior art types of electron guns and their grid configurations. In FIGURE 1 of the drawings there is shown a prior art type of electron gun 10 having a triode-grid configuration. The gun V10 includes a cathode 12, which when heated by a heater 13, will produce an electron beam 14 which is projected from the cathode 12 to a phosphor screen, not shown, of a cathode ray tube. A irst grid electrode 16 is disposed in front of the cathode 12 in such a manner as to provide a means for varying the electron emission from the cathode 12 in response to control signals applied thereto. To

produce an initial condition of electron emission from the cathode 12, the iirst grid electrode 1-6 is connected to ground potential through a lead 17, while the cathode 12 is connected to one terminal of a battery 18 through a moving contact 19 of a potentiometer 20.

After electrons have been emitted from cathode 12, they pass through an electrostatic lens provided by the grounded grid electrode 16 and a second grid electrode 22. The electrostatic lens provide a means for converging the electron beams 14 as it moves towards the phosphor screen. However, after the electron beam 14 has been converged at a point 24 it will immediately begin to diverge at an angle 0. The electron beam 14 is then accelerated on its way to the phosphor screen by means of a third grid electrode 25, which is connected to a source of high voltage 27 through a movable tap 28 of a potentiometer 29. It will also be noted that the second grid electrode 22 is connected to the high voltage source 27 through a second movable tap 36 of the potentiometer 29.

It will be understood that the angle will vary inversely in proportion to the electron beam density. That is, a density modulated electron beam such as used in video reproduction will have a divergence angle continuously varying inversely proportional to the brightness of video intelligence signals applied between the cathode 12 and first grid electrode 16.

The third grid electrode provides means for concentrating the electron density of the electron beam 14 as it moves therethrough, but it will be noted that if the electron beam 14 is initially of a lesser diameter as it enters the large aperture of the third grid electrode 25, beam concentration or focusing will be greatly improved. The electron beam having passed through the large aperture and the third grid electrode 25, which comprises the main-concentration system, will result in aberration of the more dense electron beam thereby causing the electron beam to impinge on the phosphor screen with a non-uniform focusing point. It can be seen therefore that the focusing characteristics of a more intense electron beam is poor and a so-called blooming phenomenon is caused in the reproduction of video intelligence on a phosphor screen.

The present invention overcomes the above referred to disadvantages of the prior art and a preferred embodiment is illustrated in FIGURE 2. An electron gun 40 is provided with a cathode 12 which is heated by a filament 13 thereby allowing electron emission from the cathode. The density of the electron emission from cathode 12 is controlled by a bias voltage developed between the cathode 12 and grid electrode 16 by way of the power source 18 and the potentiometer 20. A video signal input capacitor 41 has one end thereof connected to an input terminal 42 and the other end thereof connected between the cathode 12 and the movable contact 19 of potentiometer 20. The ysecond grid electrode 22 is connected to the source of the high voltage 27 through the movable contact of the potentiometer 29. According to an important feature of the present invention, an auxiliary grid electrode 45 is provided adjacent to the second grid electrode 22, as shown in FIGURE 2. The diameter of an aperture 46 of the auxiilary electrode 45 is such as to be substantially the same diameter as aperture 47 of the first grid electrode 16. The potential applied to the auxiliary grid electrode 45 is a higher potential than that applied to the second grid electrode 22, thereby forming an electrostatic lens between the second grid electrode 22 and the auxiliary grid electrode 45.

It can be seen therefore that by using the arrangement shown in FIGURE 2, the electron beam emitted from the cathode 12 will pass through the second grid electrode with a large divergence angle 0'; however, as the electron beam 14 passes through the auxiliary grid electrode 45 the divergence angle is greatly reduced to an angle 0". It has been shown, therefore, that by reducing the aperture of an auxiliary electrode `45 an initial condition of Cil divergence, or focusing, can be greatly improved, thereby improving the performance of main-concentration of an electron beam in a cathode ray tube.

As mentioned hereinabove, it was noted that not only does the aperture of the third electrode effect the divergence angle of an electron beam, but also the divergence angle is inversely proportional to the electron beam density. The graphical representation Shown in FIGURE 7 shows a curve 50 which represents electron beam current density and electron beam divergence angle Ik@ with respect to a potential difference Ek between the cathode 12 on the rst grid electrode 16. The line 51 represents a relative divergence angle 0 of an electron beam in the case where the third grid electrode is similar to that of grid electrode YZS'inTIGURE 1, andthe curve 52 represents the relative divergence angle of the electron beam in the case where an auxiliary grid electrode similar to that of the auxiliary grid is placed between the second grid electrode and the third grid electrode as Vshown in FIGURE 2. It can be seen therefore that the focusing properties of an electron beam emited from an electron gun can be greatly improved by the provision of an auxiliary grid electrode having an aperture substantially equal to the aperture of the iirst grid electrode.

As mentioned hereinabove, an inherent inadequacy of electron beam focusing is realized by the fact that the divergence angle 0' is eiected inversely proportional to the electron beam density. Therefore, when the potential difference between the cathode 12 and the first grid electrode 16 is small, the electron beam density is greatest, thereby increasing the divergence angle 0'. It is believed, that the varying divergence angle 0 is not only caused by increased electron beam density but also by a change in the convergence point 24 of electron beam 14.

To overcome the above-mentioned inherent disadvantage of large angle electron beam divergence, the present invention provides a control signal input capacitor 54 for receiving control signals from a terminal 55, which control signals are varied in accordance with video intelligence signals applied to the capacitor 41. As shown in FIGURE 2, a negative going video intelligence signal is applied to capacitor 41, while a positive going control signal, which is varying in accordance with the video signal but of opposite polarity, is applied to capacitor 54 and therefrom to the auxiliary grid electrode 45, thereby varying the potential applied to the auxiliary electrode 45 in accordance with the video intelligence signal applied to the electron gun 40. In this manner, the divergence angle 0" can be maintained at a substantially constant divergence angle independent of electron beam density as represented by curve 57 of FIGURE 7.

To better illustrate the improved characteristic of electron beam emission from the electron gun 40, consider .a condition wherein the potential difference between the cathode 12 and the rst grid electrode 16 is increased, that is, when the cathode becomes more positive than the rst grid electrode, and the beam current therefrom is decreased. This positive potential signal will cause a control voltage signal to be applied through the capacitor 54 to the .auxiliary electrode 45 thereby decreasing the potential applied thereto to allow the electron beam divergence angle 0 to increase to a constant divergence angle 0". On the other hand, when the potential difference between the cathode 12 and the first grid electrode 16 decreases, the electron beam current density will increase. This action will cause an increase potential control voltage signal to be applied to capacitor 54 thereby increasing the potential applied to auxiliary electrode 45. This, in turn, causes the divergence angle 0' to decrease to the divergence angle 0".

To better illustrate the preferred embodiment of the present invention, reference is now directed to FIGURE 8, wherein a video signal 60, having a negative polarity, is applied to the cathode input capacitor 41 of FIGURE 2. This action will cause an input control signal 61,

which has a positive polarity, to be applied to the input capacitor 54 and therefrom to the auxiliary grid electrode 45. However, it will be understood that it is also possible to provide a control signal to capacitor 54 which is of the same polarity as the signal applied to capacitor 41 `but which varies in .amplitude inverse to amplitude variations of the signal applied to capacitor 41,Y as shown `by the dotted line 60a in FIGURE 8.

It will be understood that the advantages obtained by the present invention can also be incorporated in the 'so-called grid-drive type electron gun wherein video intelligence is applied directly to the first grid electrode to control electron emission from a cathode. In this instance, as indicated in FIGURE 9, a positive video signal 63 applied to the grid electrode of an electron gun will require a positive control signal 64 to be applied to the auxiliary grid electrode of the electron gun. However, as mentioned hereinabove, it is possible to apply a negative-going signal 64a to the auxiliary grid electrode which varies inversely in amplitude to the video signal applied to the grid electrode of the cathode ray tube.

FIGURES 12 and 13 are further illustrative examples showing possible combinations of video intelligence signals of given polarity and amplitudes which can be .applied to the input of an electron gun, and further showing corresponding control voltage signals of similar or opposite polarity and amplitudes.

Shown in FIGURE 3 is an alternate type of electron gun a which heretofore has been used in some types of cathode ray tubes, and which electron gun 10a is known as a unipotential-type electron gun. In addition to the components incorporated in the electron gun 10 shown in FIGURE 1, the electron gun 10a is provided with a fourth grid electrode 66 which is connected to the high voltage source 27 via the potentiometer 29 and a slidable tap 67. Also associated with the electron gun 10a is a fifth grid electrode 70 which is electrically connected to the third grid electrode 25 by a lead 71. The electron gun 10a has the same inherent disadvantages as the electron gun 10 of FIGURE 1 in that the electron beam 14 has a relatively large divergence angle after passing through the second grid electrode 22, and which electron beam divergence angle varies inversely proportional to the electron -beam density.

An -alternate embodiment of the present invention is shown in FIGURE 4 wherein the auxiliary electrode 45 is placed between the second grid electrode 22 and the third grid electrode 25. It should also be noted, that the second grid electrode in FIGURE 4 has the shape of a flat disk and the auxiliary grid electrode 45 is cup-shaped, thereby -allowing the three grid electrodes 16, 22, and 45 to have their apertures located in a relatively close position. It should also be noted, that the aperture of the auxiliary electrode 45, FIGURE 4, has substantially the same diameter as the aperture in grid electrodes 16 and 22. By way of example, and not way of limitation, the potential applied to the grid electrode 22 may be about 300 volts, the potential applied to grids 25 and 70 .about 5000 to 30,000 volts and the potential applied to grid 66 somewhere between minus 1000 volts and plus 1000 volts.

Shown in FIGURE 5 is still another prior art type of electron gun 10b which heretofore has been used in the neck portion of some types of cathode ray tubes, and which electron gun 10b is generally known as a tripotential-type electron gun. As shown in FIGURE 5, the electron gun 10b is provided with substantially the same components as electron gun 10a of FIGURE 3 with the exception that the fifth grid electrode 70 is not provided. By way of example, and not by Way of limitation, the potentials applied to the grids 22, 25 and 66 are 300 volts, 350 volts and 5,000 to 30,000 volts respectively.

As shown in FIGURE 6, the electron gun 40b is generally of the same configuration as electron gun 10b in FIGURE 5, but is provided with the novel auxiliary grid and control of the present invention. Specifically, an auxiliary grid electrode 45 is provided between the second grid electrode 22 and the third grid electrode 25. The second grid electrode 22 is disk-shaped whereas the auxiliary grid electrode 45 is cup-shaped similar to that shown in FIGURE 4.

Shown in FIGURE 10 is still another prior -art type of electron gun 10c which heretofore has been used in some types of cathode ray tubes, ,and which electron gun 10c is known as a -bipotential-type electron gun. The electron gun 10c shown in FIGURE 10 is quite similar to the electron gun 10 shown in FIGURE 1.

FIGURE 1l illustrates a bipotential-type electron gun 40C which has incorporated therein the novel auxiliary grid 45a and control of the present invention. It is to be noted that when an auxiliary electrode 45a is used in a bipotentiabtype electron gun, it will influence the mainconcentration of the electron beam, Therefore, the aperture 46a of the auxiliary electrode 45a is made larger than the aperture of either the first grid electrode 16 or the second grid electrode 22. In this case, the auxiliary grid electrode 45a will not exert any influence upon the first grid electrode 16 and second grid electrode 22, but only effects the electrostatic lens action between the second grid electrode 22 and the third grid electrode 25.

As mentioned hereinabove, in connection with the electron gun 40, shown in FIGURE 2, the electron guns 40a, 40b and 40C are also provided with input terminals 55 to receive a varying control signal which varies in accordance with the video intelligence applied to the cathode or lirst grid electrode, thereby providing a substantially constant divergence angle of an electrode beam which is substantially independent of electron beam density. This is accomplished when the potential difference between the cathode 12 and the first grid electrode 16 is increased and the beam current therefrom is decreased in response to a video signal. This will cause the potential applied to the auxiliary grid 45 to be increased to such an extent as to decrease the potential difference between the auxiliary grid 45 and the third grid electrode 25, thereby decreasing the focusing action of the electrostatic lens formed between the grids 45 and 25. When the beam current increases, the potential of the auxiliary grid 45 is lowered to such an extent as to increase the potential difference between the auxiliary grid electrode 45 and the third grid electrode 25, thereby increasing the focusing action of the electrostatic lens formed therebetween.

It will be understood that modifications and variations may be effected Without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

1. A cathode ray tube comprising an electron gun device having at least a cathode,

a first grid electrode,

a second grid electrode,

an auxiliary grid electrode disposed adjacent to said second grid electrode but at an opposite side from which said first grid electrode is disposed,

means for applying a video signal to said electron gun,

and means for applying a control signal which is inverse to the video to said awxiliary grid electrode, the amplitude of said control signal varying in proportion to the amplitude of said video signal.

2. A cathode ray tube comprising an electrode gun device including a cathode,

a first grid electrode,

a second grid electrode,

a third grid electrode,

a fourth grid electrode,

a fifth grid electrode,

an auxiliary grid electrode placed between said second grid electrode and said third grid electrode,

said third grid electrode and said Iifth grid electrode being connected together,

means for applying a video signal to said electron gun,

means for applying a voltage to said auxiliary grid electrode,

which is modulated in accordance with said video signal, i

whereby an electron beam is produced having substantially a constant divergence angle.

3. A cathode ray tube comprising an electron gun device including a cathode,

a first grid electrode,

a second grid electrode,

a third grid electrode',

a fourth grid electrode,

a iifth grid electrode,

an auxiliary grid electrode placed between said second grid electrode and said third grid electrode.

a predetermined potential applied to said third grid electrode and said fourth grid electrode and said fth grid electrode,

said third grid electrode and said fifth grid electrode being connected together,

means for applying a video signal to said electron gun,

means for applying a voltage to said auxiliary grid electrode,

which is modulated in accordance with said video signal,

whereby an electron beam divergence angle is maintained substantially constant for varying quantities of electron beam density.

4. A cathode rray tube as claimed in claim 3, wherein the central aperture of said auxiliary grid electrode is substantially equal to the central aperture of said iirst grid electrode.

5. A cathode ray tube as claimed in claim 3, wherein said video signals are applied to said cathode, and said Video signals are of negative polarity.

6. A cathode ray tube as claimed in claim 3, wherein said video signals are applied to said auxiliary electrode, and said video signals are of positive polarity.

7. A cathode ray tube comprising `an electron gun device including a cathode,

a iirst grid electrode,

a second grid electrode,

a third grid electrode,

an auxiliary grid electrode placed between said second grid electrode and said third grid electrode,

said auxiliary grid electrode having an aperture larger than said first grid electrode,

means for applying a video signal to said electron gun,

and

a voltage applied to said auxiliary grid electrode which is modulated in accordance with said Video signal,

whereby a focusing action between said second grid electrode and said third grid electrode is maintained substantially constant and independent of electron beam density. 8. A cathode ray tube as claimed in claim 7, wherein said second grid electrode is plate-like and said auxiliary grid electrode is cup-shaped.

9. A cathode ray tube including therein an electron gun device comprising a cathode for producing a stream of electrons, at least three main grid electrodes disposed one after the other beyond said cathode, an auxiliary grid electrode disposed between said second and third grid electrodes, each of said electrodes having said electron stream pass therethrough, means for applying a fixed bias to said auxiliary grid electrode, means `for applying a video signal to said electron gun device between said cathode and said first main grid electrode, and means for applying a varying potential to said auxiliary grid electrode which varies proportionally with the amplitude of said applied video signals but having a polarity which is opposite to the polarity of said applied video signal. v10. A cathode ray tube including therein an electron gun device comprising a cathode for producing a stream of electrons, at least three main grid electrodes disposed one after the other beyond said cathode, an auxiliary grid electrode disposed between said second and third grid electrodes, each of said electrodes having said electron stream pass therethrough, means for applying a fixed bias to said auxiliary grid electrode, means for applying a video signal to said electron gun device between said cathode and said first main grid electrode, and means for applying a varying potential to said auxiliary grid electrode which varies inversely with amplitude but having the same polarity as the polarity of said applied Video signal.

References Cited UNITED STATES PATENTS 3,049,641 8/1962 Gleichauf 315-30 ROBERT L. GRIFFIN, Primary Examiner.

R. BLUM, Assistant Examiner.

U.S. Cl. XR. 

